Ceramic, multilayer graphite mold and method of fabrication



May 3, 1966 o s 3,248,763

CERAMIC, MULTILAYER GRAPHITE MOLD AND METHOD OF FABRICATION Filed March 22, 1965 FIG, .7

LPATTERN LPA TTERN I mould :51;. Z Z

wax

3,; 0 anic Poymqrvc )TZaierzaZ Gm f6 Sta 0 F; carbonacepus Dccompaslflon Pradzzcz Mouw REMOVAL colloidal Grapkiz'e Binder INVENTOR Nick 6. Lzrorzes by I in 7 dif'ys United States Patent 3,248,763 CERAMIC, MULTHLAYER GRAPHITE MOLD AND METHUD 0F FABRICATION Nick G. Lirones, North Muskegon, Mich, assignor to Howe Sound Company, New York,-N.Y., a corporation of Delaware 7 Filed Mar. 22, 1965, Ser. No. 441,827 12 Claims. (Cl. 22--129) This application is a continuation-in-part of my copending application Ser..No. 310,261, filed Sept. 20, 1963.

This invention relates to the art of casting and to materials employed in the practice of same-and it relates more particularly to the preparation of molds for use in the production of shaped products of such ditficult to cast metals as titanium, zirconium, hafnium, molybdenum, tungsten, uranium, and the like metals in Group IV-B of the periodic system.

It is an object of this invention to produce and to provide a method for producing new and improved molds for use in the casting of metals of the type heretofore described and it is a related object to provide a new and improved molding process employing same.

More specifically, it is an object of this invention to produce a mold which is of suficiently high strength and stability to enable reactive molten metals to be poured directly therein for molding to predetermined shapes; in which refractory and other metals of Group IV-b can be cast; in which such metals can be cast in a manner to minimize oxidation thereby to enable use of the process and materials in the shaping of metals that have heretofore been difficult to cast; and it is a related object to provide a new and improved molding process which can be easily carried out for the casting of metals which have heretofore not been easily adapted to casting into shaped products.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawing, in which:

FIG. 1 is a flow diagram of the process embodying the practice of this invention;

FIG. 2 is a schematic sectional view through a mold prepared in accordance with the practice of this invention; and

FIG. 3 is a schematic sectional view through the completed mold.

A mold produced in accordance with the practice of this invention embodies the novel features of inertness to minimize reactions with the metals coming intocontact with the mold surface while the metal is in a fluid state and at extremely high temperature; of generation of its own non-oxidizing atmosphere for protection of the cast molten metal;' and a material which is made 'sufliciently dense in the portions about the mold cavity to inhibit flow or infiltration of molten metal into the walls of the mold Where undesirable reactions might take place to mar the surface or finish of the cast product.

In the aforementioned copending application, description is made of the formation of a mold by repeated application of a dip coat composition and stucco in which the dip coat composition is formulated of a graphite flour and a binder of colloidal graphite and in which the stucco comprises particles of graphite whereby an all graphite mold is formed, at least in the inner portions of the mold, about the mold cavity. It has been found that when the mold is cured by heating to elevated temperature, the all graphite portions of the mold are highly absorbent such that when molten metals of the refractory types, including titanium, tantalum, zirconium, haf- 3,248,763 Patented May 3, 1966 satisfactory molding process and molded product.

In accordance with the teachings of the aforementioned application, the absorbency of the mold is reduced by treatment of the mold after cure to impregnate the mold one or more times with colloidal graphite in dilute suspension in aqueous medium. This tends to fill the spaces btween the graphite particles making up the mold walls thereby to inhibit infiltration of molten metal into the walls of the mold. While the characteristics of the mold are greatly improved by the techniques of impregnation with colloidal graphite whereby the mold becomes suitable for use in casting of reactive and refractory metals and other materials, filling of the pores to provide a barrier which makes the mold of a density to avoid penetration of the molten metal While permitting vapors to pass therethrough is diflicult to achieve with colloidal graphite alone.

The desired characteristics in a stable graphite mold can be achieved, in-accordance with the practice of this invention, by modification of the process to formulate the dip coat composition to contain, in addition to the graphite flour and colloidal graphite, a significant amount of organic polymeric material which remains to form a part of the substances remaining to form the wall portion of the mold immediately adjacent the mold cavity and which, when heated to elevated temperature, as during the cure of the mold, is thermally decomposed to carbon or a stable carbonaceous material formed in situ in the mold wall. The formed thermal decomposition product appears to give a greater effect in filling the pores in the mold walls thereby to increase the imperviousness of the mold to the penetration of molten metal but which continues to allow vapors to pass therethrough and which thus provides a barrier to the penetration of molten metal into the wall portions of the mold adjacent the mold cavity. Thus the important concept of this invention resides not only in the new and improved formulation of the composition of which the mold is formed but also in new and novel steps in the preparation and processing of the mold to produce a new and different mold having characteristics of the type described.

In the following description, the terms pattern and cluster are used interchangably to refer to a pattern 10 or cluster formed of a multiplicity of such individual patterns in which the pattern 10 comprises a material which can be removed from the mold by heat or by chemical Example 1 Preparation of the wax pattern or cluster: The pattern 10 is formed of conventional materials disposable by heat or chemicals, as in well known investment casting processes. In the illustrated modification, the pattern is molded under pressure in suitable metal molds by injection of molten wax to fill the mold and set the pattern. Instead, the pattern can be formed of a thermoplastic synthetic resinous material or combinations of such plastics and wax.

If the mold is to be formed about more than one pattern, the plurality of patterns are connected by run ners for communication with a pouring spout to form a completed cluster. Where, as in the instant process, the cluster is to be repeatedly dipped into a slurry, it is desirable to provide a hanger rod for carrying the cluster and for suspending the cluster during the drying operations.

3 Example 2 Dip coat composition Material: Percent by weight Phenol-formaldehyde (Catalin 136Catalin Corporation of America) 12.10 Isopropyl alcohol 16.0 Water 31.5

Colloidal graphite (22% solids dispersed in aqueous medium) 8.5 Gum tragacanth (3% solution in aqueous medium) 7.0 Graphite flour (less than 200 mesh) 26.0 Sodium heptadecyl sulfate (wetting agent) 1.7 Ethyl hexanol (anti-foaming agent) 4.1

As the colloidal graphite, it is preferred to make use of colloidal particles of graphite of less than 1 micron. For the purpose of reducing cost, use can be made of a combination of such colloidal graphite with up to 50% by weight and preferably up to only 30% by weight of semi-colloidal graphite having a particle size of between 120 microns.

The amount of colloidal graphite in the dip coat composition may vary but it is undesirable to make use of an amount greater than 5% by weight and it is preferred to make use of an amount within the range of 0.4% to 2% by Weight. The amount of graphite flour can vary between 15-45% by weight of the dip coat composition and it is preferred to make use of an amount within the range of 20-30% by weight of the dip coat composition.

Instead of making use of a liquid phenol formaldehyde resin, other resinous systems which are easily reducible by thermal decomposition can be employed such as furfuryl aldehyde resins, resorcinol aldehyde resins, acrylic resins, and such natural or coal tar resins as coumarone indene, turpene resins and the like. Such other synthetic resins can be employed in equivalent amounts in Example 2 with the resins being dispersed or dissolved in the dip coat composition. While not equivalent to the phenol or'furfuryl aldehyde resins, use can be made of other high polymeric organic materials which are easily thermally decomposed to carbon or to stable carbonaceous decomposition products such as others of the natural and synthetic resins, carbohydrates, proteins, albumens and the like such as sugars, starches, gums, casein and the like. In the practice of this invention, it is desirable to make use of the resinous material present in the dip coat composition in an amount within the range of 730% by weight, depending somewhat upon the amount of colloidal graphite present and it is preferred to make use of an amount of the organic decomposable material in an amount within the range of 10-20% when employed in combination with colloidal graphite binder, and from 30% when such colloidal graphite binder is absent, as will hereinafter be described.

In the dip coat compositions represented by the above formulation and the indicated modifications thereof, the emulsifying or wetting agents and the anti-foaming agents are not essential. Instead of gum tragacanth, use can be made of other hydrophilic colloids, such as gums, gelatins, alginates and the like, which when present are employed in an amount within the range of 0.01% to 0.5% by weight. Instead of the sodium heptadecyl sulphate wetting agent, other nonionic surface active agents may be employed such as the alkyl sulphates and the alkyl aryl sulfonates and their salts. When employed, the amount of surface active agent may range from 0.01% to 0.5 by weight of the composition.

Application of the dip coat composition:

The wax pattern or cluster is first inspected to remove dirt, flakes and other objects which may be adhered to the surfaces of the wax patterns and which, if allowed to remain, would impair the preparation of a good mold and lead to an imperfect casting. immersed into the dip coat composition, while being The cleaned cluster is I stirred, to cover all of the surfaces of the cluster with the exception of the lip of the pouring spout. To promote the elimination of air pockets, it is desirable to rotate the cluster while immersing in the dip coat composition. .Instead of immersing the pattern in the stirred slurry of the dip coat composition for coverage of the surfaces of the pattern, the dip coat composition can be applied to achieve the desired coverage by spraying the dip coat composition onto the surfaces of the pattern. By this latter spraying technique the coating weight of the dip coat composition can be increased or decreased, as desired, by comparison with the amount of coating retained on the surfaces by immersion.

When fully coated, the pattern or cluster is suspended to drain excess dip coat composition. During drainage, the cluster can be inspected to detect air pockets which can be eliminated by addressing a stream of air onto the uncoated portions and thereafter allowing the slurry of the dip coat composition to flow onto the uncovered areas. While the cluster is being drained, it should be held in different planes designed to achieve uniform coating on all surfaces. In general, drainage should be completed within a few minutes but, in any event, in less time than would allow the coating to dry whereby the surface would not retain stucco in the desired uniform arrangement.

Example 3 Stuccoing- After the cluster has been allowed to drain for a short time and while the surface is still wet with the dip coat composition, the surface is stuccoed with particles of graphite having the following particle size distribution.

Tyler screen size: Percent retained on screen 65 62 29 7 200 1 Pan l The graphite stucco will hereinafter be referred to as having a particle size of more than 150 mesh but less than 35 mesh. The particles of graphite are caused to flow over the surface of the pattern until the wet surface is substantially completely covered.

Application of stucco coat:

After the uniformity of coating has been achieved with the dip coat composition, the stucco is sprinkled onto the wet surface while constantly changing the position of the cluster substantially uniformly to cover the dip coating with a layer of stucco, while at the same time minimizing flow of the dip coat composition whereby non-uniformities might otherwisedevelop. In practice, the graphite particles are rained down from above through a screening member which is constantly fed from a vibratory conveyor or else applied by means of a fluidized bed. The particles of graphite adhere to the wet coating and become partially embedded therein to become integrated with the coating formed on the wax patterns.

If the dip coat composition is adjusted to enable gellation to take place within a very short period of time, the stuccoed cluster need not be set aside for drying. However, it is preferred to slow the gellation of the dip coat so that sufficient leeway is available for the desired drainage and stucco application. Thus it is desirable to provide for an air dry for a time ranging from l025 minutes. It will be understood that the drying time may be extended indefinitely beyond the times described without harm to the structure. If desired, drying of the combined coatings can be accelerated in a humidity controlled air circulating chamber heated to a temperature up to about 100 F.

The particle size of the graphite stucco is not critical since the particle size of the graphite can be varied over a fairly wide range. However, for best practice of this invention, it is preferred to make use of graphite having a particle size greater than 150 mesh and less than 20 mesh.

The operation is repeated, that is the pattern is again wet with the dip coat composition and covered with fine particles of graphite to build up a second composite layer. In the preferred practice of this invention, it is desired, though not essential, to precede the immersion of the coated pattern in the dip coat composition with a prewetting step in which the prewetting composition employs substantially the same formulation as the dip coat composition with the exception that a lower viscosity is employed, as occasoned by the formulation to include additional amounts of water suflicient to reduce the total solids to about 25-75 of the solids in the dip coat composition. Thus the coated pattern is first submerged in the prewet .composition more completely to penetrate and wet out the coated surface followed almost immediately by submersion in the dip coat composition after which the steps of drainage, stuccoing' with the fine particles of graphite, and drying are carriedv out. Thus the layers become better integrated one with the other to produce a strong and composite structure.

The steps of prewetting, if used, dip coating, stuccoing with the dry particles of graphite and drying can be repeated several times until a mold 12 of the desired thickness and strength has been built up about the disposable pattern or cluster.

,While a mold of higher strength Will be secured if the graphite particles of the type having a mesh size within the range of more than 150 but less than 20 are used throughout to build up the mold, it is preferred to make use of particles of graphite of larger dimension for use as the stucco after the second coat and preferably after the fifth coat. For such outer layers or coatings, graphite having the following particle size distribution may be employed:

Tyler screen size: Percent retained on screen 8 l 10 14 20 65 35 18 65 1 Pan 1 poured. The normal Wall thickness of mold can beachieved with the compositions described with from 5l0 cycles of dip coating, stuccoing, and drying.

Example 4 Dewaxing- After the composite mold has been produced, the disposable pattern is removed to leave a mold cavity in which the material to be molded may be cast. Pattern removal, hereinafter referred to as dewaxing, can be achieved in a number of ways:

(a) A new and novel concept in dewaxing graphite molds of the type described will hereinafter be referred to as hot'matrix dewaxing. For this purpose use is made of graphite chips preheated to an elevated temperature above the melting point temperature of the wax and preferably at least 200 F. above the melting point and more preferably to a temperature Within the range of 400-800 F. The formed mold is positioned within a flask having open ends with the crucible facing downwardly in the flask. The preheated or hot graphite particles are introduced into the flask in an amount to surround the mold. Heat is supplied from the graphite sufficient to reduce the wax of the pattern to a state for flow gravitationally from the pouring spout of the mold while the hot graphite particles, which engulf the mold as a matrix, operate also to maintain a non-oxidizing atmosphere about the graphite mold. Without removal of the mold from the flask, the assembly can be heated up to a temperature for cure of the mold as to a temperature of 2300 F. or more without deterioration of the mold thereby to enable wax removal and curing to be accomplished in a single operation for complete removal of the wax pattern and cure of the mold in a fully protected atmosphere.

Other systems for dewaxing may be employed where dewaxing is carried out as a step separate and apart from cure, as illustrated by the following:

. (b) Dewaxing can be carried out by a process referred to 'as hot sand dewaxing wherein sand heated to a temperature of 400800 F. is arranged to surround the composite for intimate contact with the outer surfaces thereof whereby rapid heat transfer is achieved into the interior to melt out the wax. The hot sand can be poured about the mold or the mold can be buried in the hot sand.

Instead of sand, use can be made of a metal or alloy system of low melting point such as the cerro alloys, low eutectic alloys, and the like.

(0) Dewaxing can be carried out with steam when the Wax patterns are formed of a material having a melting 'point range below 200 F. For such purpose, the composite can be housed within a steam chamber or autoclave or else steam at relatively high pressure can be addressed onto the composite while it is suspended with the spout extending downwardly for drainage of the molten wax.

(d) Dewaxing can be carried out in an oven heated to a temperature above the melting point temperature of the wax but below the oxidizing temperature of the graphite, or preferably at a temperature within the range of 250-800 F. in a process referred to as low temperature dewaxing, without the need to maintain a reducing atmosphere.

The next step in the fabrication of the mold is to cure the mold and thermally decompose the resinous or other high molecular weight organic compound embodied.

in the mold walls via the dip coat composition. For this purpose, the mold is heated in a non-oxidizing atmosphere to a temperature within the range of 10004300 F. for

' a time sufficient to cure the mold and to achieve the decomplete stabilization of the mold. Cure temperatures in excess of 2300 F. can be employed but the desired effect can be achieved at temperatures up to 2300 F.

The described curing and thermal decomposition steps can be carried out at the same time as dewaxing when use is made of a high temperature dewaxing method, such as in (a) above. Since graphite and the organic resinous material will be consumed when heated to a temperature above 800 F. in an oxidizing atmosphere, high temperature dewaxing, cure and decomposition are carried out in a non-oxidizing atmosphere or an inert atmosphere as under vacuum or in an atmosphere of argon, nitrogen, carbon monoxide and the like. The cured mold is cooled from elevated temperature to a safe temperature below 800 F. before exposure to atmospheric conditions for continued cooling or for further processing.

To the present, description has been made of the process and compositions wherein a mold formed substantially entirely of graphite and carbon is produced. The description will hereafter be made to the use of the new and novel graphite mold of this invention in the fabrication of shaped products of reactive and refractory or heavy metals, such as titanium, zirconium, columbium, tantalum and others of the Group IV-b metals.

Molten metal can be poured directly into the mold cavity of the graphite mold for the fabrication of cast products. The fired graphite mold possesses sufiicient strength and has sutficient mass integrity to enable the molten metal to be poured into the mold.

While preheating is not essential, it is desirable to preheat the mold prior to metal pouring. When preheated to a temperature below about 800 F. it is not necessary to preheat in a reducing or inert atmosphere, but if the graphite mold is to be preheated to a temperature above 800 F., it is essential either to preheat under vacuum conditions or in an inert or non-oxidizing atmosphere, as in an atmosphere of argon, nitrogen or carbon monoxide,

otherwise graphite will burn when exposed to oxidizing conditions. Since titanium, zirconium, tungsten, uranium and the Group IV-b metals and alloys thereof have a melting point in excess of 800 F., it is desirable to carry out metal pouring by vacuum casting techniques wherein the graphite mold, with or without preheat, is enclosed within a vacuum chamber in communication with a metal melting furnace whereby a vacuum can be drawn in the chamber in which the mold is mounted to evacuate the chamber prior to metal pouring. The mold and the metal cast therein are preferably maintained under vacuum until the metal has solidified or the assembly has cooled to a temperature below 800 F. Thereafter, the assembly can be removed from the vacuum chamber for further processing. To assist filling of the molds under vacuum, centrifugal casting techniques can be utilized while at room temperature or at elevated temperature.

An important concept of this invention resides in the ability to fabricate castings of reactive and refractory metals and alloys of extremely high melting point or metals which are subject to rapid oxidation when at elevated temperature, as represented by such metals as zirconium, silicon, tantalum, titanium, and the like. This technological advance stems in part from the new and novel characteristics made available from a graphite mold of the type produced by the practice of this invention coupled with the means and method by which the molding process is carried out. Amongst many other desirable characteristics, the graphite mold embodies high temperature stability; high dimensional stability; a desirable balance of high strength and abrasion and hot metal erosion resistance, whereby the mold maintains shape during metal pouring at high temperature without so much strength as would cause tearing of the cast product responsive to differential shrinkage upon cooling; high heat conductivity for rapid cooling or controlled heat transfer for the development of best conditions in the metal poured; and the ability to maintain an inert or reducing atmosphere for the protection of the metal while in a molten or highly oxidizable state.

This phase of the invention will be described with reference to the molding or casting of titanium, it being understood that others of the reactive and refractory or high melting point heavy metals or alloys subject to rapid oxidation at elevated temperatures may be similarly processed.

The graphite mold is transferred to the vacuum pouring furnace and the metal is poured under vacuum into the mold, with or without preheating of the mold. When preheating is employed, it is desirable to preheat the mold while under vacuum to insert the mold, but it is unnecessary to preheat to a temperature in excess of 800 F. although preheating to higher temperatures may be employed.

The poured metal is allowed to cool in the vacuum chamber or under a protective atmosphere such as argon to a temperature below that at which oxidation can take place before removal of the mold for exposure of the poured mold to the atmosphere for further cooling.

The cast metal produced can be removed by conventional techniques of impacting and shaking to break up the mold and to free the casting and by sand blasting to remove graphite retained on the surfaces of the casting.

Thermal reduction of the organic resinous component of the dip coat composition depends upon the maintenance of a non-oxidizing atmosphere during the heating to elevated temperature, otherwise the organic resinous material would burn to be consumed and removed from the system. The formed decomposition product operates not only to produce a mold section which is impervious to the molten metal but it also contributes to some extent the characteristics of a high temperature binder to build strength into the cured mold.

The concepts of this invention can also be achieved in the use of a dip coat composition in which the colloidal graphite is absent and in which its binder function is replaced by additional amounts of organic resinous or high molecular weight materials which function as an interim binder until the mold is heated to elevated temperature for thermal decomposition of the resinous or high molecular weight organic material to produce carbon or a stable form of carbonaceous material.

The following are representative of dip coat compositions formulated without colloidal graphite and which may be used as the dip coat composition instead of Example 2:

Example 5 Material Percent by weight Liquid phenol formaldehyde resin (Catalin 136) 27 Isopropyl alcohol 35 Graphite flour (less than 20 mesh) 38 Example 6 Liquid phenol formaldehyde resin (Catalin 8944) 26 Distilled Water 35 Graphite flour (less than 200 mesh) 39 When still greater densities are desired in the mold walls about the mold cavity, the dried mold before firing or the fired mold can be impregnated one or more times with a dilute solution (0.5-10 percent by weight) of an organic resinous or high polymeric material of the type employed in the dip coat composition followed by firing in a non-oxidizing atmosphere to a temperature in excess of 800 F. or the dried or fired mold can be impregnated one or more times with a dilute dispersion (0.5-5 percent by weight) of colloidal graphite followed by firing at an elevated temperature in excess of 800 F. in a non-oxidizing atmosphere.

It will be understood that changes may be made in the details of construction, arrangement and operation without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. In the method of producing a mold about a disposable pattern which is removed to define the mold cavity and in which the mold is adapted for use in the casting of metals of the group IV-b in the periodic system, the steps of wetting the surfaces of the pattern with an aqueous dip coat composition the solids of which consist essentially of graphite flour, colloidal graphite and an organic high molecular weight material which is thermally decomposable at elevated temperature and in a non-oxidizing atmosphere to a stable form of a material selected from the group consisting of carbon and a carbonaceous material in which the graphite flour is present in an amount within the range of 1545 percent by weight, the colloidal graphite is present in an amount up to 5 percent by weight and the organic high molecular weight material is present in an amount within the range of 7-30 percent by weight, covering the surfaces of the pattern wet with the dip coat composition with a graphite stucco, repeating the application of dip coat composition and stucco for a number of cycles with intermediate drying to build up a wall thickness about the pattern forming at least a part of the mold wall, removing the pattern and firing the mold to a temperature in excess of 800 F. in

anon-oxidizing atmosphere to cure the mold and thermally to reduce the organic high molecular weight material to the carbonaceous reduction reaction product in situ in the walls of the mold to produce a mold in which the wall portions about the mold cavity are relatively impervious to molten metal but which enables vapors to pass therethrough.

2. The method as claimed in claim 1 in which the organic high polymeric material is an organic resinous material.

3. The method as claimed in claim 1 in which the organic high polymeric material is a phenol-aldehyde resm.

4-. The method as claimed in claim 1 in which the organic high polymeric material is an organic compound selected from the group consisting of a carbohydrate, a protein and an albumen.

5. The method as claimed in claim 1 in which the organic high molecular weight material is present in an amount within the range of to 20 percent by weight.

6. The method as claimed in claim 1 in which the colloidal graphite is present in an amount within the range of 0.4 to 2.0 percent by weight.

7. The method as claimed in claim 1 in which the graphite flour is present in an amount within the range of 20 to 30 percent by weight.

8. The method as claimed in claim 1 in which the organic high molecular weight material is a synthetic phenolaldehyde resin and is present in an amount within the range of 10 to 20 percent by weight, and in which the colloidal graphite is present in an amount within the range of 0.4 to 2.0 percent by weight and the graphite flour is present in an amount within the range of 20 to 30 percent by weight.

9. The method as claimed in claim 1 which includes the step of impregnating the cured mold with a dilute solution of an organic resinous material in which the organic resinous material is thermally decomposable at 10 elevated temperature, followed by the heating of the mold to elevated temperature thermally to decompose the resinous material.

10. The method as claimed in claim 1 which includes the step of impregnating the cured mold with colloidal graphite in dilute dispersion in aqueous medium further to fill the pores of the mold.

11. A mold produced by the method of claim 1 in which the wall portion of the mold about the mold cavity is composed essentially of carbonaceous materials consisting of graphite flour, graphite stucco and interbonded with colloidal graphite and the carbonaceous thermal decomposition product of a synthetic organic polymeric material in which the elements are present in the ratio of 7-40 parts by weight of the organic thermal decomposition product, up to 5 parts by weight of colloidal graphite and l545 parts by weight of graphite flour.

12. A mold produced by the method of claim 1 in which the wall portion of the mold about the mold cavity is composed essentially of carbonaceous materials con 'sisting of graphite flour, graphite stucco and interbonded with colloidal graphite and the carbonaceous thermal decomposition product of a synthetic organic polymeric material in which the elements are present in the ratio of 10-20 parts by weight of the organic high polymeric decomposition product, 0.4-2.0 parts by weight of colloidal graphite and 1030 parts by weight of graphite fiour.

References Cited by the Examiner UNITED STATES PATENTS 2,564,308 8/1951 Nagel 22192 2,806,271 9/1957 Operball 22196 2,886,869 5/1959 Webb et al.

3,005,244 10/1961 Erdle 22196 3,153,824 10/1964 Holmes 22192 3,153,826 10/1964 Horton 22-192 MARCUS U. LYONS, Primary Examiner. 

1. IN THE METHOD OF PRODUCING A MOLD ABOUT A DISPOSABLE PATTERN WHICH IS REMOVED TO DEFINE THE MOLD CAVITY AND IN WHICH THE MOLD IS ADAPTED FOR USE IN THE CASTING OF METALS OF THE GROUP IV-B IN THE PERIODIC SYSTEM, THE STEPS OF WETTING THE SURFACES OF THE PATTERN WITH AN AQUEOUS DIP COAT COMPOSITION THE SOLIDS OF WHICH CONSIST ESSENTIALLY OF GRAPHITE FLOUR, COLLOIDAL GRAPHITE AND AN ORGANIC HIGH MOLECULAR WEIGHT MATERIAL WHICH IS THERMALLY DECOMPOSABLE AT ELEVATED TEMPERATURE AND IN A NON-OXIDIZING ATMOSPHERE TO A STABLE FORM OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF CARBON AND A CARBONCEOUS MATERIAL IN WHICH THE GRAPHITE FLOUR IS PRESENT IN AN AMOUNT WITHIN THE RANGE OF 15-45 PERCENT BY WEIGHT, THE COLLOIDAL GRAPHITE IS PRESENT IN AN AMOUNT UP TO 5 PERCENT BY WEIGHT AND THE ORGANIC HIGH MOLECULAR WEIGHT MATERIAL IS PRESENT IN AN AMOUNT WITHIN THE RANGE OF 7-30 PERCENT BY WEIGHT, COVERING THE SURFACES OF THE PATTERN WET WITH THE DIP COAT COMPOSITION WITH A GRAPHITE STUCCO, REPEATING THE APPLICATION OF DIP COAT COMPOSITION AND STUCCO FOR A NUMBER OF CYCLES WITH INTERMEDIATE DRYING TO BUILD UP A WALL THICKNESS ABOUT THE PATTERN FORMING AT LEAST A PART OF THE MOLD WALL, REMOVING THE PATTERN AND FIRING THE MOLD TO A TEMPERATURE IN EXCESS OF 800*F. IN A NON-OXIDIZING ATMOSPHERE TO CURE THE MOLD AND THERMALLY TO REDUCE THE ORGANIC HIGH MOLECULAR WEIGHT MATERIAL TO THE CARBONACEOUS REDUCTION REACTION PRODUCT IN SITU IN THE WALLS OF THE MOLD TO PRODUCE A MOLD IN WHICH THE WALL PORTIONS ABOUT THE MOLD CAVITY ARE RELATIVELY IMPERVIOUS TO MOLTEN METAL BUT WHICH ENABLES VAPORS TO PASS THERETHROUGH. 